A ferromagnetic body means a material that is spontaneously magnetized even though a strong magnetic field is not applied thereto from the outside. In a magnetic tunnel junction structure (first magnetic body/insulator/second magnetic body) in which an insulator is interposed between two ferromagnetic bodies, an electric resistance varies depending on relative magnetization directions of two magnetic layers, i.e., a tunnel magnetoresistance (TMR) effect occurs. The TMR effect occurs because up-spin and down-spin electrons flow at different degrees at the magnetic tunnel junction structure while tunneling an insulator.
According to the law of action and reaction that is Newton's third law of motion, if the magnetization direction may control a flow of current, it is also possible to control a magnetization direction of the magnetic layer by applying current due to the reaction. If current is applied to the magnetic tunnel junction structure in a direction perpendicular to a film surface, the current spin-polarized by a first magnetic body (magnetization pinned magnetic layer, hereinafter referred to as “pinned magnetic layer”) transfers its spinning angular momentum while passing through a second magnetic body (magnetization free magnetic layer, hereinafter referred to as “free magnetic layer”). A torque felt by magnetization due to the transfer of spinning angular momentum is called a spin-transfer torque (STT). Use of the spin-transfer torque make it possible to fabricate a device for reversing the free magnetic layer or continuously rotating the free magnetic layer or a device for moving a magnetic domain wall of the free magnetic layer.
Moreover, the magnetic tunnel junction may lead to magnetization reversion of a free magnetic layer or movement of a magnetic domain structure by using a spin-orbit torque (SOT) generated by spin Hall effect or Rashba effect when in-plane current flows in a conducting wire adjacent to the free magnetic layer.
A magnetization reversing device using a spin-orbit torque is disclosed in U.S. Pat. No. 8,416,618 B2.
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